Angiopoietins are expressed in the normal rat pituitary gland

Interaction of vascular endothelial growth factor (VEGF) with the angiopoietins (Ang) is an essential component of angiogenesis. Localization of VEGF in the anterior pituitary raises the possibility that Ang must be present in the pituitary gland as well. In this study Ang expression was detected in the normal rat pituitary gland at the gene level by reverse-transcriptase polymerase chain reaction and at the protein level by immunohistochemistry. The latter was analyzed by both light and confocal microscopy. Constitutive expression of Ang1, Ang2, and their receptor Tie2 was detected at both the mRNA and protein level in all the pituitary glands studied. Of interest was the localization of both Ang1 and Ang2 in scattered PAS positive adenohypophysial cells rather than in endothelial cells. Confocal microscopy showed colocalization of both Ang1 and Ang2 proteins within the same adenohypophysial cells. Dual immunostaining for Ang1 and the anterior pituitary hormones that show PAS positivity demonstrated colocalization of Ang1 with follicle stimulating hormone and luteinizing hormone. In the posterior pituitary, strong Ang1 signal observed in vascular endothelial cells masked the weak Ang2 signal, a pattern that is similar to that reported in brain endothelial cells. The presence of both angiopoietins and VEGF in the pituitary gland suggest that these ligands interact during angiogenesis as they are known to do in other systems to maintain the rich vascular network of the gland. This first report of angiopoietin localization in the rat pituitary gland opens a new line of investigation on angiogenesis in pituitary glands that will impact human endocrinology in the future.